The proposed research focuses on the synthesis and subsequent biological evaluation of eight novel polyribonucleotides. The polymers are analogs of polycytidylic acid (poly C) and polyuridylic acid (poly U) in which the substituent at the 2-position of the base moiety is varied. Complexing the polymers with polyinosinic acid (poly I) or polyadenylic acid (poly A) and observing the effect the 2-substituent has on (1) antitumor activity, (2) interferon induction, (3) resistance to the degradative effect of nucleases, and (4) duplex stability, will provide information that may lead to an understanding of the factors that synthetic polynucleotides must possess in order to trigger antitumor or antiviral activity and offer resistance to nucleases. Synthetic procedures are outlined for the preparation of the necessary nucleosides, nucleotides, and nucleoside-5'-diphosphates. The diphosphates will be enzymatically polymerized using polynucleotide phosphorylase bound to an insoluble support. The polymers will be characterized, complexed with appropriate complementary polynucleotides, and evaluated for biological activity.